C. William Kilpatrick, a professor of biology at the University of Vermont, shows some mice that were trapped around the state this fall on Dec. 3. / GLENN RUSSELL/FREE PRESS

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Free Press Staff Writer

With winter fast approaching, people may have forgotten how warm and snow-free last winter was.

That is, until the mice start invading.

Mice loved last winter, and the warm spring and dry summer that followed. In such favorable conditions the mice had lots of babies, which may now be trying to get into your house to escape the cold.

In some parts of Vermont, there are signs there might be two or three times the normal number of deer mice running around, said C. William Kilpatrick, a University of Vermont biology professor who studies the rodents.

Kilpatrick monitored mouse trapping sites in five Vermont locations over the summer, two in Addison County, two in the Northeast Kingdom and one in the northern Green Mountains.

Typically, when he checks the sites, one in 10 traps has caught a mouse. That was true in two of the sites he studied in the summer. But at three sites, one in Addison County and the two Northeast Kingdom sites, two or three of 10 traps had caught mice, he said.

That’s an indication there’s plenty of extra mice out there.

People responding to a Free Press inquiry on Facebook told their own stories of battling a mouse population boom.

“We have lived in our house in South Strafford for 22 years. We have never had a year like this. Probably by a factor of 10. And that belief is shared by all our neighbors,” wrote Jill Michaels. “We need a Pied Piper.”

Christopher LeBlanc of Morrisville said his property has a lot of mice, too. “They have been in our vehicles in our garage. We even ended up getting one in our fridge. We still can’t figure that one out,” LeBlanc said.

He said lately, ermines, a type of weasel, have been around his house and have been feeding on mice. LeBlanc is a new fan of the weasel. Said he: “Go ermines!”

Why the mice?

Several factors came together to give Vermont the mouse boom, said Kilpatrick and pest control experts. Last winter was mild, so harsh weather didn’t kill them. The spring and summer were warm and dry, which create great breeding conditions, said Jon Quackenbush, owner of South Hero-based PestPro.

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“It’s a very good year for mice. Not so good for homeowners,” Quackenbush said.

Another factor is invasive plant species, like honeysuckle, which offer mice protection from predators like hawks and owls, Kilpatrick said.

Mice always try to find someplace warm when it gets cold, so there’s an annual invasion of the critters into homes, garages and sheds this time of year, Quackenbush said.

Banish the house mouse

There’s plenty of reasons why you don’t want mice in your house. They can harbor deer ticks, which can spread Lyme disease. However, Kilpatrick said it’s unlikely for a person to get Lyme disease from a mouse in his or her home. You’re more apt to get it in the grass and weeds outside.

Mice even carry a very slight risk of spreading the potentially dangerous hantavirus, according to the Vermont Department of Health. Health officials suggest avoiding contact with rodents and their droppings, just in case.

Despite that Health Department admonition, many people take a do-it-yourself approach to getting rid of mice. Some hardware stores in northwestern Vermont report brisk sales of traps and poisons such as d-CON.

“Every day, people come in and want a mousetrap,” said Nate Chates of the St. Albans Ace Hardware. “We’ve been running out on a regular basis because we can’t keep up.”

The stampede for mouse control products hasn’t been as intense at other stores. Sales of traps and poisons at the Aubuchon Hardware in Milton picked up this fall, but not dramatically so, said Walt Tummons, the manager of the store.

The story was the same at Bibens Lakeshore Ace Hardware and Marine in Colchester, where Assistant Manager Doug Mayo said he’s only seen a slight increase in trap sales. The real rush was in insect killer, because of a rash of box elder bug invasions into people’s homes in the late summer and autumn, he said.

A more effective way of preventing mice from enjoying your warm home is to block their access, which is difficult because deer mice can squeeze into a crack the circumference of a pencil, Quackenbush said.

Quackenbush suggests removing accumulated leaves near foundations. Mice can use the protection of the leaves as a staging area before finding a crack through which to enter your home.